This invention relates to intershaft bearings of the type utilized for supporting coaxially mounted shafts interconnecting the compressors and turbines of a multi-spool gas turbine engine and particularly to means for stabilizing the viscous damper.
As is well known in the art an inherent vibratory instability can exist in a multi-shaft rotor system which is connected by a viscous (oil) damper. This instability is similar to the well known "oil whip" which is experienced on high speed rotating machinery which incorporates plain journal bearings. The instability results from the development of a rotating pressure field when one shaft spins. This pressure can excite the natural frequency of the other shaft and force the system into high, uncontrollable vibration.
We have found that we can obviate the problem noted above and eliminate this instability from the operating speed range of the first shaft by raising the natural frequency of the second shaft with a spring mounted in parallel with the viscous damper. This spring can either be a metal structure or an elastomeric one. Thus, in accordance with this invention incorporated between two rotating shafts the damper can be made to perform properly without producing unstable, high amplitude response.